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Effects of building aspect ratio,diurnal heating scenario,and wind speed on reactive pollutant dispersion in urban street canyons

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Journal of Environmental Sciences 2012年第12期24卷 2091-2103页

作者： Nelson Y.O.Tong Dennis Y.C.Leung Department of Mechanical Engineering The University of Hong Kong

A photochemistry coupled computational fluid dynamics （CFD） based numerical model has been developed to model the reactive pollutant dispersion within urban street canyons, particularly integrating the interrelationship among diurnal heating scenario （solar radiation affections in nighttime, daytime, and sun-rise/set）, wind speed, building aspect ratio （building-height-to-street-width）, and dispersion of reactive gases, specifically nitric oxide （NO）, nitrogen dioxide （NO2） and ozone （O3） such that a higher standard of air quality in metropolitan cities can be achieved. Validation has been done with both experimental and numerical results on flow and temperature fields in a street canyon with bottom heating, which justifies the accuracy of the current model. The model was applied to idealized street canyons of different aspect ratios from 0.5 to 8 with two different ambient wind speeds under different diurnal heating scenarios to estimate the influences of different aforementioned parameters on the chemical evolution of NO, NO2 and 03. Detailed analyses of vertical profiles of pollutant concentrations showed that different diurnal heating scenarios could substantially affect the reactive gases exchange between the street canyon and air aloft, followed by respective dispersion and reaction. Higher building aspect ratio and stronger ambient wind speed were revealed to be, in general, responsible for enhanced entrainment of 03 concentrations into the street canyons along windward walls under all diurnal heating scenarios. Comparatively, particular attention can be paid on the windward wall heating and nighttime uniform surface heating scenarios.

关键词： photochemistry reactive pollutant dispersion building aspect ratio diurnal heating scenario wind speed urban streetcanyon

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Physio-chemical modeling of the NO_(x)-O_(3) photochemical cycle and the air pollutants’ reactive dispersion around an isolated building

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建筑模拟(英文) 2023年第9期16卷 1735-1758页

作者： Yunfei Fu Xisheng Lin Xing Zheng Liangzhu Wang Chun-Ho Liu Xuelin Zhang Cruz Y.Li K.T.Tse Department of Civil and Environmental Engineering The Hong Kong University of Science and TechnologyClear Water BayKowloonHong KongChina Future Cities Lab Global Singapore-ETH CentreSingapore 138602 Department of Building Civil and Environmental Engineering at Concordia UniversityMontrealQuebecCanada Department of Mechanical Engineering The University of Hong KongPok-fu-lam RoadHong KongChina Department of Civil Engineering Chongqing UniversityChongqingChina School of Atmospheric Sciences Sun Yat-sen UniversityZhuhaiChina

A numerical physio-chemical model of the NO_(x)-O_(3) photochemical cycle in the near-wake region of an isolated residential/office building has been presented in this *** investigation delves into the dispersion of reactive air pollutants through the lens of fluid phenomenology and its impact on chemical reactivity,formation,transport,deposition,and *** fluid dynamics(CFD)simulations were conducted for the ground-point-source(GES)and roof-pointsource(RES)*** show that the Damköhler number(Da),which quantifies pollutants’physio-chemical timescales,displays a strong inverse proportionality with the magnitude and spread of NO–increasing Da reduces human exposure to the toxic NO and NO_(2) *** different wind directions were considered,the dispersion range of NO exhibited varying shrinking directions as Da ***,as Da increases,the concentration ratio KNO_(2)/KNO_(x),which quantifies the production of NO_(2) resulting from NO depletion,forms sharp high-low gradients near emission *** GES,the dispersion pattern is governed by the fluid’s phenomenological *** RES,the intoxicated area emanates from the building’s leading-edge,with the lack of shielding inhibiting pollutant interactions in the near-wake,resulting in scant physio-chemical *** NO_(2)/NO_(x) distribution follows a self-similar,stratified pattern,exhibiting consistent layering gradients and attributing to the natural deposition of the already-reacted pollutants rather than in-situ *** the end,building design guidelines have been proposed to reduce pedestrian and resident exposure to NO_(x)-O_(3).

关键词： reactive pollutant dispersion NO_(x)-O_(3)cycle air pollution isolated building physio-chemical modelling

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